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United States Patent |
6,177,103
|
Pace
,   et al.
|
January 23, 2001
|
Processes to generate submicron particles of water-insoluble compounds
Abstract
Submicron particles of water-insoluble compounds, particularly drugs, are
prepared by simultaneously stabilizing microparticulate suspensions of
same with surface modifier molecules by rapid expansion into an aqueous
medium from a compressed solution of the compound and surface modifiers in
a liquefied gas and optionally homogenizing the aqueous suspension thus
formed with a high pressure homogenizer.
Inventors:
|
Pace; Gary W. (Raleigh, NC);
Vachon; Michael G. (Quebec, CA);
Mishra; Awadhesh K. (Quebec, CA);
Henrikson; Inge B. (Stavanger, NO);
Krukonis; Val (Lexington, MA)
|
Assignee:
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RTP Pharma, Inc. (Durham, NC)
|
Appl. No.:
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335735 |
Filed:
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June 18, 1999 |
Current U.S. Class: |
424/489 |
Intern'l Class: |
A61K 009/14 |
Field of Search: |
424/489
|
References Cited
U.S. Patent Documents
3998753 | Dec., 1976 | Antoshkiw et al. | 252/312.
|
5922355 | Jul., 1999 | Parikh et al. | 424/489.
|
Foreign Patent Documents |
0 744 992 B1 | Dec., 1996 | EP.
| |
WO 95/21688 | Aug., 1995 | WO.
| |
WO 97/14407 | Apr., 1997 | WO.
| |
WO 98/07414 | Feb., 1998 | WO.
| |
WO 99/52504 | Oct., 1999 | WO.
| |
Other References
G. Donsi et al. Pharm. Acta Helv, 1991, pp. 170-173, "Possibility of
Application to Pharmaceutical Field".
|
Primary Examiner: Dodson; Shelley A.
Assistant Examiner: George; Konata M.
Attorney, Agent or Firm: Nixon & Vanderhye
Parent Case Text
This application claims benefit to provisional 60/089,852 filed Jun. 19,
1998.
Claims
What is claimed is:
1. A process of preparing a stable suspension of sub-micron particles of a
water-insoluble or substantially water-insoluble biologically active
compound of up to 2000 nm in size comprising the successive steps of:
(a) dissolving a water-insoluble or substantially water-insoluble
biologically active compound and a first surface modifier in a liquefied
compressed gas solvent therefor and forming a solution of greater than 1%
w/w of said compound in said solvent and thereafter;
(b) expanding the compressed fluid solution prepared in step (a) into water
or aqueous solution containing a second surface modifier and water-soluble
agents thereby producing a suspension of microparticles, and thereafter
(c) homogenizing the suspension of step (b) at high pressure.
2. The process according to claim 1, including the additional step of (d)
recovering the microparticles so produced.
3. The process according to claim 1, wherein the first surface modifier and
the second surface modifier are the same.
4. The process according to claim 1, wherein the first surface modifier and
the second surface modifier are different.
5. The process according to claim 1, wherein one or both of the surface
modifiers is a phospholipid.
6. The process according to claim 1, wherein one or both the surface
modifiers is a surfactant.
7. The process of claim 1 wherein one or both of the surface modifiers is a
mixture of two or more surfactants.
8. The process according to claim 1, wherein at least one surface modifier
is a surfactant devoid or substantially completely devoid of phospholipid.
9. The process of claim 6 wherein the surface modifier is a polyoxyethylene
sorbitan fatty acid ester, a block copolymer of ethylene oxide and
propylene oxide, a tetrafunctional block copolymer derived from sequential
addition of ethylene oxide and propylene oxide to ethylenediamine, an
alkyl aryl polyether sulfonate, polyethylene glycol, hydroxy
propylmethylcellulose, sodium dodecylsulfate, sodium deoxycholate,
cetyltrimethylammonium bromide or combinations thereof.
10. The process of claim 5 wherein the surface modifier is of egg or plant
phospholipid or semisynthetic or synthetic in partly or fully hydrogenated
or in a desalted or salt phospholipid such as phosphatidylcholine,
phospholipon 90 H or dimyristoyl phosphatidylglyerol sodium salt,
phosphatidylethanolamine, phosphatidylserine, phosphatidic acid,
lysophospholipids or combinations thereof.
11. The process of claim 1 wherein the compound is a cyclosporine,
fenofibrate, or alphaxalone.
12. The process of claim 1 wherein the particles produced are less than 500
nm in size.
13. The process of claim 12 wherein the particles produced range from 5 up
to about 200 nm in size.
14. The process of claim 1 wherein 99% of the particles produced are below
2000 nm.
15. The process of claim 1 wherein the liquefied compressed gas is carbon
dioxide in the supercritical or sub-critical phase.
Description
This invention provides processes for producing micrometer and
sub-micrometer sized particulate preparations of biologically useful
compounds that are water-insoluble or poorly water-soluble, particularly
water-insoluble pharmaceutical agents.
BACKGROUND AND SUMMARY OF INVENTION
A major problem in formulating biologically active compounds is their poor
solubility or insolubility in water. For instance, over one third of the
drugs listed in the United States Pharmacopoeia are either water-insoluble
or poorly water-soluble. Oral formulations of water-insoluble drugs or
compounds with biological uses frequently show poor and erratic
bioavailability. In addition, drug insolubility is one of the most
recalcitrant problems facing medicinal chemists and pharmaceutical
scientists developing new drugs. Water-insolubility problems delay or
completely block the development of many new drugs and other biologically
useful compounds, or prevent the much-needed reformulation of certain
currently marketed drugs. Although the water-insoluble compounds may be
formulated by solubilization in organic solvents or aqueous-surfactant
solutions, in many cases such solubilization may not be a preferred method
of delivery of the water-insoluble agent for their intended biological
use. For instance, many currently available injectable formulations of
water-insoluble drugs carry important adverse warnings on their labels
that originate from detergents and other agents used for their
solubilization.
An alternative approach for the formulation of water-insoluble biologically
active compounds is surface-stabilized particulate preparations. Small
particle size formulation of drugs are often needed in order to maximize
surface area, bioavailability and, dissolution requirements. Pace et al.
("Novel Injectable Formulations of Insoluble Drugs" in Pharmaceutical
Technology, March 1999) have reviewed the usefulness of the
microparticulate preparations of water-insoluble or poorly soluble
injectable drugs.
In U.S. Pat. Nos. 5,091,187 and 5,091,188 to Haynes describe the use of
phospholipids as surface stabilizers to produce aqueous suspension of
submicron sized particles of the water-insoluble drugs. These suspensions
are believed to be the first applications of the surface modified
microparticulate aqueous suspension containing particles made up of a core
of pure drug substances and stabilized with natural or synthetic bipolar
lipids including phospholipids and cholesterol. Subsequently, similar
delivery systems exploiting these principles have been described (G. G.
Liversidge et al., U.S. Pat. No. 5,145,684; K. J. Illig et al. U.S. Pat.
No. 5,340,564 and H. William Bosch et al., U.S. Pat. No. 5,510,118)
emphasizing the usefulness of the drug delivery approach utilizing
particulate aqueous suspensions.
In U.S. Pat. No. 5,246,707 Haynes teaches uses of phospholipid-coated
microcrystals in the delivery of water-soluble biomolecules such as
polypeptides and proteins. The proteins are rendered insoluble by
complexation and the resulting material forms the solid core of the
phospholipid-coated particle.
These patents and others utilized processes based on the particle size
reduction by mechanical means such as attrition, cavitation, high-shear,
impaction, etc achieved by media milling, high pressure homogenization,
ultrasonication, and microfluidization of aqueous suspensions. However,
these particle size reduction methods suffer from certain disadvantage,
such as long process duration (high-pressure homogenization or
microfluidization) and contamination (media milling, and ultrasonication).
In addition, these methods may not be suitable for aqueous suspensions of
compounds with limited stability in aqueous medium at the pH, high
temperature and high pressure conditions prevailing in these processes.
Among the alternatives that address to these problems is a procedure which
uses liquefied gasses for the production of microparticulate preparations.
In one such method liquefied-gas solutions are sprayed to form aerosols
from which fine solid particles precipitate. The phenomenon of solids
precipitated from supercritical fluids was observed and documented as
early as 1879 by Hannay, J. B. and Hogarth, J. "On the Solubility of
Solids in Gases," Proc. Roy. Soc. London 1879 A29, 324,
The first comprehensive study of rapid expansion from a liquefied-gas
solution in the supercritical region was reported by Krukonis (1984) who
formed micro-particles of an array of organic, inorganic, and biological
materials. Most particle sizes reported for organic materials, such as
lovastatin, polyhydroxyacids, and mevinolin, were in the 5-100 micron
range. Nanoparticles of beta-carotene (300 nm) were formed by expansion of
ethane into a viscous gelatin solution in order to inhibit post expansion
particle aggregation. Mohamed, R. S., et al. (1988), "Solids Formation
After the Expansion of Supercritical Mixtures," in Supercritical Fluid
Science and Technology, Johnston, K. P. and Penninger, J. M. L., eds.,
describes the solution of the solids naphthalene and lovastatin in
supercritical carbon dioxide and sudden reduction of pressure to achieve
fine particles of the solute. The sudden reduction in pressure reduces the
solvent power of the supercritical fluid, causing precipitation of the
solute as fine particles.
Tom, J. W. and Debenedetti, P. B. (1991), "Particle Formation with
Supercritical Fluids--a Review," J. Aerosol. Sci. 22:555-584, discusses
rapid expansion of supercritical solutions techniques and their
applications to inorganic, organic, pharmaceutical and polymeric
materials. This technique is useful to comminute shock-sensitive solids,
to produce intimate mixtures of amorphous materials, to form polymeric
microspheres and deposit thin films.
Most studies of rapid expansion from supercritical solution on organic
materials utilize supercritical carbon dioxide. However, ethane was
preferred to carbon dioxide for beta-carotene because of certain chemical
interactions. Carbon dioxide is generally preferred, alone or in
combination with a cosolvent. Minute additions of a cosolvent can
significantly influence the solvent properties. When cosolvents are used
in rapid expansion from a supercritical solution, care is required to
prevent de-solution of the particles due to solvent condensing in the
nozzle. Normally, this is achieved by heating the supercritical fluid,
prior to expansion, to a point where no condensate (mist) is visible at
the nozzle tip.
A similar problem occurs when carbon dioxide is used. During adiabatic
expansion (cooling), carbon dioxide will be in two phases unless
sufficient heat is provided at the nozzle to maintain a gaseous state.
Most investigators recognize this phenomenon and increase the
pre-expansion temperature to prevent condensation and freezing in the
nozzle. A significant heat input is required (40-50 kcal/kg) to maintain
carbon dioxide in the gaseous state. If this energy is supplied by
increasing the pre-expansion temperature the density drops and
consequently reduces the supercritical fluid's solvating power. This can
lead to premature precipitation and clogging of the nozzle.
The solvent properties of liquefied-gas are strongly affected by their
fluid density in the vicinity of the fluid's critical point. In rapid
expansion from liquefied-gas solutions, a non-volatile solute is dissolved
in a liquefied-gas that remains either in the supercritical or
sub-critical phase. Nucleation and crystallization are triggered by
reducing the solution density through rapid expansion of the liquefied-gas
to atmospheric conditions. To achieve this the liquefied-gas is typically
sprayed through 10-50 micron (internal diameter) nozzles with aspect
ratios (L/D) of 5-100. High levels of supersaturation result in rapid
nucleation rates and limited crystal growth. The combination of a rapidly
propagating mechanical perturbation and high supersaturation is a
distinguishing feature of rapid expansion from a liquefied-gas solution.
These conditions lead to the formation of very small particles with a
narrow particle size distribution.
There are a number of advantages in utilizing compressed carbon dioxide in
the liquid and supercritical fluid states, as a solvent or anti-solvent
for the formation of materials with submicron particle features. Diffusion
coefficients of organic solvents in supercritical fluid carbon dioxide are
typically 1-2 orders of magnitude higher than in conventional liquid
solvents. Furthermore, carbon dioxide is a small linear molecule that
diffuses more rapidly in liquids than do other antisolvents. In the
antisolvent precipitation process, the accelerated mass transfer in both
directions can facilitate very rapid phase separation and hence the
production of materials with sub-micron features. It is easy to recycle
the supercritical fluid solvent at the end of the process by simply
reducing pressure. Since supercritical fluids do not have a surface
tension, they can be removed without collapse of structure due to
capillary forces. Solvent removal from the product is unusually rapid. No
carbon dioxide residue is left in the product, and carbon dioxide has a
number of other desirable characteristics, for example it is non-toxic,
nonflammable, and inexpensive. Furthermore, solvent waste is greatly
reduced since a typical ratio of antisolvent to solvent is 30:1.
Exploiting these concepts Henriksen et al. in WO 97/14407, disclosed a
process using compressed fluids to produce sub-micron sized particles of
water insoluble compounds with biological uses, particularly water
insoluble drugs by precipitating a compound by rapid expansion from a
supercritical solution in which the compound is dissolved, or
precipitating a compound by spraying a solution, in which the compound is
soluble, into compressed gas, liquid or supercritical fluid which is
miscible with the solution but is antisolvent for the compound. In this
manner precipitation with a compressed fluid antisolvent (compressed fluid
antisolvent) is achieved.
An essential element of this process is the use of phospholipids and other
surface modifiers to alter the surface of the drug particles to prevent
particle aggregation and thereby improve both their storage stability and
pharmacokinetic properties. This process combines or integrates
phospholipids or other suitable surface modifiers such as surfactants, as
the aqueous solution or dispersion in which the supercritical solution is
sprayed. The surfactant is chosen to be active at the compound-water
interface, but is not chosen to be active at the carbon dioxide-organic
solvent or carbon dioxide-compound interface when carbon dioxide is used
as the supercritical solution. The use of surface modifying agents in the
aqueous medium allowed making submicron particles by the compressed fluid
antisolvent process without particle aggregation or flocculation.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a graph showing the size distribution (relative volume v.
particle size in nm) of cyclosporine produced in Example 3, and
FIG. 2 is a graph showing the size distribution (relative volume v.
particle size in nm) of cyclosporine produced in Example 4, and
BRIEF DESCRIPTION OF THE INVENTION
However, this prior process suffered from a very long duration of spray of
the supercritical solution to obtain a substantial quantity of the desired
product. The long duration of spray-process may be attributed to a slow
rate of association of the surface modifier molecules or their assemblies
in the aqueous medium with the newly precipitated solute particles.
During experimentation with the process of WO 97/14407 described above it
was surprisingly found that incorporation of a surface modifier in both
the supercritical (or sub-critical) liquefied gas along with incorporation
of a surface modifier in the water insoluble substance allowed one to
achieve a very rapid production of surface stabilized nanometer- to
micrometer-sized particulate suspensions. The principle feature of the
present invention is believed to be rapid attainment of intimate contact
of the dissolved drug and the surface modifier during the very fast
precipitation step of the drug from their solution in the liquefied gas.
While very rapid precipitation is a characteristic of precipitation of
solutes from liquefied gases, the rapid intimate contact with the surface
modifier is achieved by having the surface modifiers dissolved in the
liquefied-gas containing the dissolved drug. A rapid intimate contact
between the surface modifier and the newly formed particle substantially
inhibits the crystal growth of the newly formed particle. In addition, if
the surface modifier(s) is not included with the dissolved drug the rate
at which the liquefied-gas droplet containing the drug is brought into
contact with the anti-solvent is much slower if very small stable
particles are to be obtained. Thus a key feature of the invention is the
high productivity of the process.
Although at least one (first) surface modifier should be dissolved along
with the water insoluble substance to be reduced in size in the liquefied
gas in the inventive process, additional (second) surface modifying agents
of the same or different chemical nature may also be included in the
aqueous medium. Further, during or after precipitation the fluid streams
may be subjected to additional high shear forces, cavitation or turbulence
by a high-pressure homogenizer to facilitate intimate contact of the
particle surface and the surface modifier. Thus, in those cases where all
the surface modifier is dispersed in the aqueous medium and the liquefied
gas contains only the water insoluble substance, additional high shear
forces, cavitation or turbulence by a high-pressure homogenizer can be
exploited to facilitate the intimate contact of the particle surface and
the surface modifier.
Thus, the overall objective of the present invention is to develop a
process with high productivity based on the use of liquefied gas solvents,
including supercritical fluid technology, that yields surface modifier
stabilized suspensions of water insoluble drugs with an average particle
size of 50 nm to about 2000 nm and a narrow size distribution. The process
is robust, scalable and applicable to a wide range of water-insoluble
compounds with biological uses.
DETAILED DESCRIPTION OF THE INVENTION
The present invention includes procedures for using super critical or
compressed fluids to form surface modified particles of up to about 2000
nm in size and usually below 1000 nm, desirably less than 500 nm,
preferably less than about 200 nm and often in a range of 5 to 100 nm in
size. The size of the particles refers to volume weighted mean diameters
of these particles suspended in aqueous medium.
The process of the present invention includes forming aqueous
microparticulate suspensions of water insoluble or poorly water soluble
compounds while simultaneously stabilizing of same with surface modifier
molecules by rapid expansion into an aqueous medium from a compressed
solution of the compound and surface modifiers in a liquefied-gas (Rapid
Expansion of Liquefied Gas Solution, RELGS).
Alternatively another embodiment of the invention includes forming aqueous
microparticulate suspensions of water insoluble or poorly water soluble
compounds while simultaneously stabilizing the same with surface modifier
molecules by rapid expansion into an aqueous medium of a compressed
solution of the compound and surface modifiers in a liquefied-gas and
homogenizing the aqueous suspension thus formed with a high pressure
homogenizer (Rapid Expansion of Liquefied-Gas Solution and Homogenization,
RELGS-H).
While not wishing to be bound by any particular theory, the processes of
this invention are believed to induce rapid nucleation of the
liquefied-gas dissolved drugs and other biologically active substances in
the presence of surface modifying agents resulting in particle formation
with a desirable size distribution in a very short time. Phospholipids or
other suitable surface modifiers such as surfactants, as may be required,
may be integrated into the processes as a solution or dispersion in the
liquefied gas. In addition, the surface modifier may or may not be
incorporated via its solution or dispersion in the aqueous medium.
Alternatively, some of the surface modifiers may be dissolved in the
liquefied gas along with the water insoluble substance and expanded into a
homogenized aqueous dispersion of rest of the surface modifier of the
formulation. The introduction of suitable surface modifying agents in the
above noted processes serves to stabilize the generated small particles
and suppress any tendency of particle agglomeration or particle growth
while they are formed.
By industrially useful insoluble or poorly soluble compounds we include
biologically useful compounds, imaging agents, pharmaceutically useful
compounds and in particular drugs for human and veterinary medicine.
Usually, the water insoluble compounds are those having a poor solubility
in water, that is less than 5 mg/mL at a physiological pH of 6.5 to 7.4,
although the water solubility may be less than 1 mg/mL and even less than
0.1 mg/mL.
Examples of some preferred water-insoluble drugs include immunosuppressive
and immunoactive agents, antiviral and antifungal agents, antineoplastic
agents, analgesic and anti-inflammatory agents, antibiotics,
anti-epileptics, anesthetics, hypnotics, sedatives, antipsychotic agents,
neuroleptic agents, antidepressants, anxiolytics, anticonvulsant agents,
antagonists, neuron blocking agents, anticholinergic and cholinomimetic
agents, antimuscarinic and muscarinic agents, antiadrenergic and
antiarrhythmics, antihypertensive agents, antineoplastic agents, hormones,
and nutrients. A detailed description of these and other suitable drugs
may be found in Remington's Pharmaceutical Sciences, 18th edition, 1990,
Mack Publishing Co. Philadelphia, Pa.
A range of compressed gases in the supercritical or sub-critical fluid
phases have been reported in the prior art (for example, U.S. Pat. No.
5,776,486, and Tom, J. W. and Debenedetti, P. B. (1991), "Particle
Formation with Supercritical Fluids--a Review," J. Aerosol. Sci.
22:555-584) from which a suitable gas may be selected for the purpose of
the present invention. These include but are not limited to gaseous oxides
such as carbon dioxide and nitrous oxide; alkanes such as ethane, propane,
butane, and pentane; alkenes such as ethylene and propylene; alcohols such
as ethanol and isopropanol; ketones such as acetone; ethers such as
dimethyl or diethyl ether; esters such as ethyl acetate; halogenated
compounds including sulfur hexafluoride, chlorofluorocarbons such as
trichlorofluoromethane (CCl.sub.3 F, also known as Freon 11),
dichlorofluoromethane (CHCl.sub.2 F, also known as Freon 21),
difluorochloromethane (CHClF.sub.2, also known as Freon 22), and
fluorocarbons such as trifluoromethane (CHF.sub.3, also known as Freon
23); and elemental liquefied gases such as xenon and nitrogen and other
liquefied compressed gases known to the art.
Liquefied carbon dioxide was used to prepare rapid expansion solutions of
the drugs described in the following examples. Carbon dioxide has a
critical temperature of 31.3 degrees C. and a critical pressure of 72.9
atmospheres (1072 psi), low chemical reactivity, physiological safety, and
relatively low cost. Another preferred supercritical fluid is propane.
Examples of some suitable surface modifiers include: (a) natural
surfactants, such as casein, gelatin, natural phospholipids, tragacanth,
waxes, enteric resins, paraffin, acacia, gelatin, and cholesterol, (b)
nonionic surfactants such as polyoxyethylene fatty alcohol ethers,
sorbitan fatty acid esters, polyoxyethylene fatty acid esters, sorbitan
esters, glycerol monostearate, polyethylene glycols, cetyl alcohol,
cetostearyl alcohol, stearyl alcohol, poloxamers, polaxamines,
methylcellulose, hydroxycellulose, hydroxy propylcellulose, hydroxy
propylmethylcellulose, noncrystalline cellulose, and synthetic
phospholipids, (c) anionic surfactants such as potassium laurate,
triethanolamine stearate, sodium lauryl sulfate, alkyl polyoxyethylene
sulfates, sodium alginate, dioctyl sodium sulfosuccinate, negatively
charged phospholipids (phosphatidyl glycerol, phosphatidyl inosite,
phosphatidylserine, phosphatidic acid and their salts), and negatively
charged glyceryl esters, sodium carboxymethylcellulose, and calcium
carboxymethylcellulose, (d) cationic surfactants such as quaternary
ammonium compounds, benzalkonium chloride, cetyltrimethylammonium bromide,
and lauryldimethylbenzyl-ammonium chloride, (e) colloidal clays such as
bentonite and veegum, (f) natural or synthetic phospholipid, for example
phosphatidylcholine, phosphatidylethanolamine, phosphatidylserine,
phosphatidylinositol, phosphatidylglycerol, phosphatidic acid,
lysophospholipids, egg or soybean phospholipid or a combination thereof.
The phospholipid may be salted or desalted, hydrogenated or partially
hydrogenated or natural semisynthetic or synthetic. A detailed description
of these surfactants may be found in Remington's Pharmaceutical Sciences,
18th Edition, 1990, Mack Publishing Co., PA; and Theory and Practice of
Industrial Pharmacy, Lachman et al., 1986.
The following examples further explain and illustrate the invention:
EXAMPLE 1
Phase Behavior of Water Insoluble Compound in Compressed Liquefied Gasses.
In order to assess whether a particular water insoluble compound should be
formulated as an aqueous submicron particulate suspension from its
solution in the liquefied gasses, the solubility of the candidate drugs in
the liquefied gasses was measured.
To prepare solutions with a constant molar composition, measured amounts of
drug (fenofibrate) were charged to a constant volume view cell.
Temperature was kept constant at 60.degree. C. Pressure was varied from
1300 to 4000 psi by pumping the compressed liquefied gas into the view
cell. The phase behavior was determined visually by noting the pressure at
which the solid drug appeared to dissolve. A summary of fenofibrate
solubility in liquefied carbon dioxide, propane and ethane is given in
Table I. The solubility values of >1% w/w in any solvent would allow the
fine-particulate preparation from these solvents.
TABLE I
Fenofibrate Solubility Experiment in Liquefied Carbon Dioxide,
Propane and Ethane at 60.degree. C.
Liquefied gas Pressure (psi) Solubility (%, w/w)
Carbon Dioxide 1800 0.01
2000 0.08
2800 1.4
Propane 1500 2.5
2000 2.3
Ethane 1300 0.016
2000 0.79
3000 1.80
4000 1.90
EXAMPLE 2
Fenofibrate Microparticle Formation by the RELGS Process
A solution containing Fenofibrate (2 g), Lipoid E-80 (0.2 g), Tween-80 (0.2
g) in the liquefied carbon dioxide pressurized to 3000 psi was expanded
through a 50 mm orifice plate into water held at atmospheric pressure and
room temperature (22.degree. C.). A fine suspension of fenofibrate was
obtained with a mean particle size of about 200 nm. The particle sizing
was performed by photon correlation spectroscopy using Submicron Particle
Sizer-Autodilute Model 370 (NICOMP Particle Sizing Systems, Santa Barbara,
Calif.). This instrument provides number weighted, intensity weighted, and
volume weighted particle size distributions as well as multi-modality of
the particle size distribution, if present.
EXAMPLE 3
A fine spray-nozzle was constructed with PEEK capillary tubing of an
internal diameter of 63.5 mm. This PEEK nozzle was fastened with a M-100
Minitight male nut and attached to an Upchurch SS20V union body which was
further attached to a 1/4 inch high pressure manifold via Swagelok.TM.
brand fittings of appropriate size. Except for the PEEK tubing all other
components were made up of 316 stainless steel. A liquefied gas solution
of the water insoluble substance was introduced at high pressure (>1000
psig) through the 1/4 inch high pressure manifold into the 63.5 mm PEEK
nozzle to be expanded into the aqueous medium. The vessel for the
liquefied gas solution was charged with 1 g of cyclosporine and 0.2 g of
Tween-80. The vessel was filled with carbon dioxide at 5000 psig and
heated to about 24.degree. C. The vessel was allowed to stand for about 20
minutes for complete dissolution and for attaining equilibrium.
Separately, a 2% w/w suspension of egg phospholipid (Lipoid E80 from
Lipoid GmbH) in a 5.5% solution of mannitol was homogenized at 6000 psi
with an Avestin Emulsiflex C50 homogenizer (Avestin Inc, Ottawa, Canada)
for 15 min when it produced a clear dispersion. The pH of the phospholipid
suspension was adjusted to 8.0 with aqueous NaOH solution prior to
homogenization. The carbon dioxide solution of cyclosporine and Tween-80
that was held at 24.degree. C. and 5000 psig was expanded into the aqueous
dispersion of egg phospholipid. Very rapidly, in about 3 minutes, a
translucent aqueous suspension of about 23 nanometer particle size was
obtained (See FIG. 1). This example provides a simple scalable process by
the way of incorporation of several such PEEK nozzles within a manifold
and simultaneously expanding into a reservoir containing appropriate
amount of the aqueous medium. The PEEK nozzle is known to be inert and
very inexpensive. Construction of the nozzle is very simple and can be
done in less than 10 minutes.
EXAMPLE 4
Cyclosporine Microparticle Formation by the RELGS-H Process
An aqueous suspension containing Mannitol (5.5%), Lipoid E-80 (2%), and
Tween 80 (2%), was prepared. A solution of cyclosporine in the Liquifed
gas was also prepared and kept at 2000 psig and 60.degree. C. This
solution was expanded through a 63.5 mm PEEK nozzle into the aqueous
suspension. A suspension of about 3 g cyclosporine was made in this way.
The resulting suspension was homogenized for 8 passes at 6,000 psig. The
final mean particle size after homogenization was 86 nanometers with the
99 percentile at 150 nm (see FIG. 2) as measured using the Submicron
Particle Sizer-Autodilute Model 370 (NICOMP Particle Sizing Systems, Santa
Barbara, Calif.).
While the invention has been described in connection with what is presently
considered to be the most practical and preferred embodiment, it is to be
understood that the invention is not to be limited to the disclosed
embodiment, but on the contrary, is intended to cover various
modifications and equivalent arrangements included within the spirit and
scope of the appended claims.
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